Insulation piercing wire connector



July 22, 1952 M. D. BERGAN 2,604,503

INSULATION PIERCING WIRE CONNECTOR Filed Nov. 19, 194'? J L.. 3 H 23 241 I F B l3 a afafiaa==l w 3 WW r :1 .5. A E :1 INVENTOR.

MARTIN D. BERGAN w wozrm ATTORNEY Patented July 22, 1952 INSULATIONPIERCING WIRE CONNECTOR Martin D. Bergan, Westfield, N. J., assignor toThe Thomas & Betts 00., Elizabeth, N. J., a corporation of New JerseyApplication November 19, 1947, Serial No. 786,901

3 Claims. (01. 174-84) The invention relates in general to an insulationpiercing wire connector and specifically relates to connectors of thetubular type into the bores in which cables are inserted and theconnectors distorted into a crimping engagement with the cables.

It is known in the prior art of cable coupling connectors to strip backthe insulation on an end of a cable to expose the conductor wiresforming the core of the cables, to introduce the stripped back ends ofthe cable into the bore of a metal sleeve and crimp the sleeve on to theexposed ends of the cables. It has also been suggested to roughen thebore in difierent ways to enhance the gripping effect of the sleeve onto the cable and its conductors.

, In my copending application, Serial No. 618,218, filed September 24,1945, now Patent No. 2,480,280, granted August 30, 1949 I suggestedthreading the bore of a connector with a spiral thread constructed tobite into the exposed strands of the conductor forming core of a cablefrom which the insulation is stripped back. The known form of connectorsare dimensioned to engage cables of a size sufficiently large so thatthe stripping back of the insulation did not present any greatdlfiiculty.

} There has recently come on the market a form of cable of extremelysmall diameter known as magnet wire, one form of which includes a coreformed of a copper wire inclosed in a coating of varnish, and in somecases a thin tube of enamel, in both cases forming an insulation andwhich enamel tube or varnish coating is in turn closely wrapped with alayer of cotton or silk thread. It is extremely diificult to strip backthe insulation of these small size conductors due, among other things,to the fact that the enamel for instance is tough and resistant to beingstripped from the metal core but primarily due to the difficulty ofholding these small conductors especially in the field often without theequipment necessary to hold small wire.

The primary object of the invention is to provide an improved techniquein making a mechanical and electrical connection between a metallicsleeve and an insulating covering therefor, in such way that the cableinsulation is not stripped back and an electric connection over arelatively large area of contact is made as an i'ncident'of followingthe conventional practice of distorting the sleeve into a crimpingengagement with the cable inserted into the bore of the sleeve.

, Broadly this objective is'attained by providing the bore of the sleevewhich is to form the connector, or at least that portion of the borewhich subsequently becomes involved in the crimping operation, with aplurality of closely related inwardly pointing sharp points arranged ina substantially uniformly distinctive pattern and proportioned to pierceand penetrate the insulation over an extensive area and to intrude moreor less into the electric wire or wires forming the core of the cableand at the same time to provide for an extensive area of electriccontacting engagement between the sides of the projections and the wirestrands which go to make up the wire cores and to do this withoutnecessity of preparing the cable ends to enter the connector.

More specifically defined the bore of the tubular connector is tapped toprovide a spiral V-thread therein and is slotted longitudinally with V-shaped slots, circumferentially spaced to form with the thread acheckerboard pattern of pointed projections, each of four sidedpyramidal form with their rectangular bases contacting in edgeto-edgerelation.

Various other objects and advantages of the invention will be in partobvious from an inspection of the accompanying drawings and in part willbe more fully set forth in the following particular description of oneform of connector embodying the invention, and the invention alsoconsists in certain new and novel features of construction andcombination of parts hereinafter set forth and claimed.

In the accompanying drawings the several figures are very muchexaggerated in size over the parts illustrated in order to show detailsnot easily visible to the eye and in which:

Fig. 1 is a view partly in elevation and partly in axial section of atubular connector constituting a preferred embodiment of the inventionand shown inoperative engagement crimped on to a pair of cables;

Fig. 2 is a view in axial section of the connector blank and associatedcables of Fig. 1 before being crimped into its final position to formthe connector of Fig. 1;

Fig. 3 is a transverse section of the assembly shown in Fig. 1, somewhatenlarged and taken on the line 3-3 of Fig. 1;

Fig. 4 is an axial section of the right end portion of the connectorblank shown in Fig. 2 with the extreme right end portion both splinedand tapped, and the adjacent left end portion splined but not yettapped;

Fig. 5 is a transverse sectional view of the connector blank taken onthe line 55 of Fig. 4}

Fig. 6- is an enlarged view of the bore wall suraeogsoe face shown inthe proceeding figures and laid flat to show the checkerboardarrangement of the pyramidal teeth;

Fig. 7 is an enlarged showing of a portion of the disclosure in Fig. 1,illustrating two opposing axial lines of the pyramidal teeth penetratingopposite sides of the insulation and biting into a single wireconductor, and

Fig. 8 is a view similar to the upper portion of Fig. 7 and showing aline of the pyramidal teeth penetrating the insulation and piercing intoa conductor of the stranded wire type.

In the drawings and referring first to the complete assembly ofconnectors and cables in Fig. 1, there is disclosed a tubular connectorl in its final form in crimped engagement with the cables to beconnected thereby. Into opposite ends of the bore ii there is disposedcables A and B in approximate end-to-end-relation and with opposite endsof the connector'distorted into a crimping engagement with-the intrudedends of both cables to secure them mechanically and electrically to theconnector and therethrough to each other.

The wires or cables A and B are each of the magnet wire type andspecifically are of the type known as formex insulation magnet wire.

The cables are of identical construction and include in the case ofFigs. 1, 2, 3 and '7 a single copper wire C forming the core. In theshowin of Fig. 8 the conductor core D is a strand of very fine wirestwisted together to form a bundle. The core is inclosed within a layerof insulation extremely thin relative to the core. The insulationillustrated is an enamel baked on to the wire core. It is within thescope of the disclosure to make the insulation of certain types ofplastic insulating material containing resins, and a thermosettingvarnish containing a formaldehyde derivative is suggested.

The magnet wires as now sold on the market are usually wrapped with anouter layer F of insulating fibrous material such as cotton, silk andsometimes paper.

It is noted that in this case the insulation E and F about the conductorcore is not cut back as has been usual in such situations. The cablesare simply cut oil to provide the squared off ends G and the insulationextends solidly to the ends of the cables in the form manufactured andsold on the market. Referring to the blank tube or sleeve from which theconnector I0 is formed it will be understood that initially it is simplyan open end cylindrical sleeve provided with a smooth bore extendingaxially therethrough from end-to-end. This sleeve is formed of any ofthe malleable metals usually used for crimping on to conductorscontained therein and in the instant case the sleeve is formed of softcopper but aluminum would be equally indicated.

The distinctive feature of this disclosure is that the surface definingthe wall of the bore is formed of a plurality of sharp pointedprojections arranged in closely adjacent relation to form in effect anapproximately checkerboard pattern. These projections are formed byslotting the bore wall to provide a series of splines 12 as shown at theleft end of Fig. 4, and shown to be V-shaped in cross section andequidistantly spaced apart circumferentially of the bore as shown inFig. 5, forming V-shaped troughs l3 therebetween. The bore wall soslotted is tapped to provide a spiral thread I extending from end-to-endof the sleeve and forming V-shaped troughs l between adjacent turns ofthe thread. The threads and the splines are each of sixty degreesincluded angle. The troughs between the splines and the troughs betweenthe turns of the thread mutually intersect each other at an angle, asshown in Figs. 4 and 6, of about eighty-five degrees and thus aresubstantially at right angles to each other. This machining of the walldefining the bore of the sleeve forms the wall into regularly anduniformly spaced apart rows and columns of substantially pyramidal teethIS. The base ll of each tooth as shown by the heavy lines in Fig. 6outlining one of the teeth marked 18 is substantially square or moreaccurately is an equilateral parallelogram. The bases of the teeth abutin edge-to-edge relation so that the bore is formed entirely of teethwith no blank spaces therebetween. Each tooth is defined by four sidesl9-20-2l and 22, each side being of triangular form; is symmetrical withits axis which extends radially inwardly and with its apex forming asharp point 23 directed to the axis a b of the bore. More specificallydescribed, the four sides form two wedges, whose opposing sides are inintersecting planes forming an incluuded angle of about sixty degreesand which four sides form the sharply pointed apex. Differentlyconsidered the bore is formed in elfect by a large number of sharppoints 23 equidistantly spaced apart, opposing sides of the teeth, forinstance the opposing sides l9 and 2|, form in effect wedgesprogressively increasing in their contacting areas with the conductors Cand D as the bases H are approached.

In the form of the invention'shown in Fig. l, but not in the form shownin Fig. 2, it is suggested that after the bore has been machined asabove described the stock sleeve thus formed be indented at its centerto provide a pair of center stops 24--25 to limit the insertion of thecables into the opposite ends of the bore H as is usual in this art.

In general it will be understood that outwardly of the stops 24-25 inboth directions therefrom, the sharp points 23 coact to define acylinder whose cross section closely approaches the cross section of thecables A and B and sufiiciently over-size to permit the cables to beinserted freely into the bore II with a sliding fit and withoutintentional injury to the fibrous wrapping F. The cables are inserteduntil the stops 24-45 resist any further advance. Opposite ends of theconnector [0 are then subjected to the action of any suitable 'form ofcrimping tool to form crimps H and I to distort the connector into abinding engagement with both cables and incidentally change each end ofthe connector, from its original circular form into an hexagonalrform asshown in Fig. 3;

Considering the action of each tooth IS with reference to a single wireC it will be appreciated that in moving from the initial position shownin Fig. 2 into the final position shown in Figs. 1, 3 and 7, the pointedapices operate to penetrate first the fibrous covering F and then theinsulation E. In passing through the threads forming the covering F itsappears that adja-' cent threads are simply pushed apart withoutnecessarily being cut and are crowded into the troughs 15. This radialsqueezing of the connector is continued until the pointed apices 23.

engage in metal-to-metal electric contact with the conductor core C. Ofcourse, any further contractions of the bore ll will cause the points 23to bite more or less into the surface of the wire 0- as shown in Fig. 7.Under the squeeze force present, the sharp points 23 easily breakthrough the outer surface of the insulation E and as soon as eachbreak'is made, the two wedges of the associated tooth begin to come intooperation and force the insulating material in advance of the inwardly:moving teethoutwardly in all directions and into the troughs I3 and 15.As the insulation E is thin and somewhat plastic it can easilyaccommodate itself into any available space and is undoubtedly compactedand perhaps has lost some of its insulating characteristics, but withinthe connector insulation is, of course, not desired.

In the case where a stranded form of core wire is used the advance endsof the teeth It tends to work themselves into and between the strandswhich form the outside of the core D as shown in Fig. -8 and in this waythe advanced portions of the teeth tend to make electric contact withsome of the internal strands and the wedging sides of the teeth tend tomake an extensive metal-to-metal contact with the several strands asthey become separated by the inwardly advanced teeth. In the showing inFig. 8, the teeth l6 have penetrated the wrapping forming the outerlayer F, have pierced through the enamel insulating coating E, haveseparated two outside strands, one of which is shown at J and arebearing on an inner strand K in a tendency to buckle it at the pointscontacted. It is not so much the individual tooth action which isimportant here, as it is the aggregate coaction of many teeth whenconsidered in their closely grouped relation. It is appreciated that thegreatest possible area of contacting surface must be provided betweeneach cable core or conductor and the metal connector and this becomesparticularly necessary in the instant device which features smallall-over dimensions.

The porcupine, stippled or nutmeg grater effect presented by thegripping points of the bore has the effect of engaging even initially,closely positioned spots over the entire area of the conductor core andthese localized spots, of course. each increase in contacting areaasmore and more of their wedging sides in distinction from thesharppoints engage the conductor or conductors as the case may be.

In actual practice and despite the fact that there are remnants of theinsulation E and F remaining within the connector, still tests show thatthe resistance between the connector and. conductor is not materiallymore than would be the case if there was solely a metal-to-metal contactbetween conductor and connector. Apparently the increase in surfacecontact provided by the four wedging surfaces l9-22 compensates for anyinsulating effect presented by the remnants of the insulations.

As so far described it is assumed that the teeth I 6 have that degree ofhardness which is inherent in the original stock material of which theconnector is made with such increase in hardness as may be imposedthereon by the machining incidental to the slotting and threading of thebore as herein featured.

There are situations encountered in this art where the conductor wiresare hard or medium hard drawn and thus the teeth herein featured must beof a hardness equal to or greater than that of the wire in those caseswhere it is desired to have the teeth bite into th conductors assuggested in Fig. 7.

It is accordingly suggested that an even greater degree of hardness mayb imposed on the teeth especially when the blank is made of a ferrousmetal such as steel. This can be done by electro-plating the outersurface of the tubular blank with a protective coating, say of copper,and then heat treating .the toothed bore in a cyanide or carbonizingbath to harden the bore and thus the teeth. This method is more fullydisclosed in my application Serial No. 759,241, filed July 5, 1947,entitled Case-Hardened Cable Connector. In this way there is provided aconnector in which the teeth, particularly in the pointed apex thereof,may have any desired degree of hardness while the connector consideredas a whole retains its original relatively soft ductile condition andthus may be easily crimped as above described.

I claim:

1. A one-piece connector formed of malleable steel and provided With apreformed bore fashioned to receive a magnet wire of the type whichincludes a conductor having an enamel insulating jacket baked thereonand to have the connector deformed into a crimping engagement with theconductor in the bore of the magnet wire, at least a portion ofthelength of the bore wall being formed solely of rugged teeth havingsharp pointed, hardened apices equidistantly spaced apart in twodirections, considered both longitudinally and circumferentially of thebore, and forming a uniformly stippled area defining a conductor contactsurface of cylindrical form, the teeth being each of pyramidal form withsubstantially square bases arranged in contact in a regular geometricpattern of thread-like spiral columns and straight parallel rows withthe columns and rows in intersecting relation and forming a checkerboarddesign completely covering said portion of the bore and in which eachtooth forms the center tooth of a group of five teeth and is reinforcedand buttressed at all four sides of its base by the engagement therewithof the four teeth surrounding it, the four sides of each tooth formingtwo Wedges whose opposing sides are in intersecting planes forming anincluded angle of about sixty degrees and the intersection of whichsides form its hard, sharply-pointed apex, the axis of each toothextending substantially in a radius of said cylindrical contact surface,each side of each tooth forming a V-shaped trough with the adjacent sideof the next tooth considered in any direction so that the toothedportion of the bore Wall is formed entirely by the inwardly facing sidesof the teeth, the aggregate area of said teeth being greater than thearea of said toothed portion of the bore wall, and which teeth coact toform said portion of the bore wall as a checkerboard design of inwardlyfacing teeth and inwardly facing troughs, each of said troughs havingmaximum depth opposite the apices of the pair of teeth forming thetrough adapted to receive that portion of the enamel which is displacedinto the same by the associated pair of teeth and said troughs havingtheir least depth Where each corner of one tooth base meets the cornersof the three adjacent teeth bases.

2. In a device of the class described, the combination of a one-piecetubular connector of ductile metal, a magnet wire including a conductoron which is baked an enamel jacket intruded into an end of the bore ofthe connector, at least a portion of the bore which contains the magnetwire defined entirely by a set of sharply pointed teeth of pyramidalform with substantially rectangular bases and arranged in a regulargeometric pattern of spiral columns and parallel 7 rows'intersecting toform the teeth and eachtooth forming a trough between itself and'thenext adjacent tooth, considered in anyrdirection and each of whichtroughs is V-shaped in -cross section, of maximum depth .at itsmid-length and decreasing in depth towards its opposite ends,

said connector being crimped onto the magnet wire with thesharply-pointed apex ends of the teeth radially penetrating the layerforming the enamel jacket and in electric contact with :the conductor atuniformly spaced-apart points on all sides of the conductor, the portionof the enamel between adjacent 'pairs of teeth, considered in directionsat right angles to each other, adhering to the conductor and theportionof'the enamel displaced by each tooth being crowded into thespace considered radially between the enamel so adheringto the conductorand the'bottom of its associated trough.

3. A one-piece sleeve formed of a malleable metal having capacityfor'electric conductivity and adapted to be deformed intoa-crimping'engagement with the conductor core of an insulated cableinserted in its bore, the wall defining the bore of the sleeve, in atleast a. part thereof designed to be so deformed, formed completely of abank of sharply-pointed inwardly extending teeth with their apicesdefining a closed cylinder,

each tooth being :of pyramidal form :and said REFERENCES CITED The'following'references are of record in the file'o'f this patent:

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